The Energy Information Administration’s (EIA) U.S. Crude Oil, Natural Gas, and Natural Gas Liquids Proved Reserves, 2008 reports that proved reserves of crude oil fell by more than 10 percent in 2008, primarily because of low end-of-year prices used to estimate proved reserves, even though discoveries of crude oil rose for the third year in a row. In contrast, proved reserves of natural gas rose by 3 percent in 2008, despite low end-of-year prices.

Proved reserves are those volumes that geological and engineering data demonstrate with reasonable certainty to be recoverable from known reservoirs under existing economic and operating conditions. Under Securities and Exchange Commission (SEC) rules in effect since 1982, operators assessed their 2008 proved reserves based on the market price on the last day of the year.

Crude Oil. The end-of-year crude oil price for 2008 - $44.60 per barrel for West Texas Intermediate (WTI) crude oil - was less than half the end-of-year price for 2007 - $95.95 per barrel. As a result, operators reported record negative net revisions of more than 2 billion barrels to their proved reserves estimates, more than they produced during the year.

Under updated SEC rules issued in 2008 that take effect in 2010, operators will instead use an annual average of first-day-of-the-month prices to develop their reserves estimates. This average price will be less sensitive to volatility in prices. The SEC's new rules would have shown an increase in oil prices from $71.79 per barrel in 2007 to $101.63 per barrel in 2008, a 42 percent price increase rather than the significant decline operators actually used. Under the new rules, there would likely have been a smaller drop (or possibly even an increase) in crude oil proved reserves.